The natural man deduces and then produces. He employs his gifts to dig, gather, perceive and analyze. Then, he attempts to reproduce what seems right. He does the best he can.
The spiritual man receives and then reveals. The man or woman yielded to the Spirit opens his heart to the things of the Kingdom of God. God speaks or discloses His mysteries, His secrets, His living truth to him. Now he simply believes and displays what he's already seen and heard.
It's not guesswork because God Himself has opened His realities to His servant. Through humility and discipline he learns to hear His voice. He then confidently calls to be that which he now knows is in the heart and mind, intention and behavior of the living God.
Jesus declared that He only said what he heard the Father say and only did what he saw the Father do. So, what means Paul by saying, we walk by faith and not by sight? The very best the natural man can do is to have a perception, an analysis and an assessment that is sorted out by his own natural faculties. The man of faith cannot operate merely by what he sees and hears in the natural. He must operate by the revelation and disclosure of the Father and Son (Word) by the Holy Spirit.
What no eye has seen, nor ear heard,
nor the heart of man imagined,
what God has prepared for those who love him—
these things God has revealed to us through the Spirit.